(1) Field of the Invention
This invention relates to a process for preparing an indole by subjecting an aniline and an ethylene glycol to a gas-phase catalytic reaction at a superatmospheric pressure
(2) Description of the Prior Art
Indoles have been known as raw materials for the chemical industry and the importance of indole in particular has increased in recent years as raw materials for the syntheses of fragrant substances and amino acids.
A number of attempts have heretofore been made with a view toward synthetically obtaining indoles. However, these attempts were all accompanied by one or more of such problems as many by-products being produced, expensive raw materials being required and multiple step preparation processes being necessary.
Recently, there have been found catalysts effective for reactions in which indoles can be synthesized using anilines and ethylene glycols, inexpensive raw materials, through single step processes (see, for example, Japanese Patent Laid-open Nos. 46865/1981, 110672/1981 and 150062/1981). However, use of such catalysts have been accompanied by such problems as undergoing severe activity reduction due to deposition of hydrocarbons and the like on their surfaces and frequent regeneration and activation treatments being necessary in order to have the catalysts regain their activity.